Jacko,
I appreciate your passion for an "R5" Nimrod, but the three prototype MRA4 airframes can still be upgraded to operational MRA4 configuration. I know that this hasn't happened yet, but sanity will at some prevail - possibly post SDR 2010.
"R5" precludes this - making RC-135 a good choice irrespective of the the "commonality with the USAF" arguments. And I for one have no whatsoever faith that BAES could deliver an "R5" programme to time or on budget.
S41